The present invention relates to a steering device, particularly relates to a rack and pinion steering device which transmits a steering force exerted to a steering wheel to a side of a wheel by way of a rack that is brought in mesh with a pinion.
There is a rack and pinion steering device which transmits a steering torque of a steering wheel to a side of a wheel by way of a rack that is brought in mesh with a pinion. Further, there is a rack and pinion steering device which has a steering force assisting device (electric power steering device) which makes manipulation of a steering wheel easy by detecting a steering torque of the steering wheel, assisting a steering force exerted to the steering wheel, and transmitting the steering force to a side of a wheel by way of a rack that is brought in mesh with a pinion. As such steering devices, there are rack and pinion steering devices which are disclosed in Japanese Unexamined Patent Publication No. 2010-038254 and Japanese Unexamined Patent Publication No. 2010-031915.
FIG. 10 is a perspective view showing a total of a rack and pinion steering device in a related art, FIG. 11 is a front view of a pinion shaft of FIG. 10, and FIG. 12 is a perspective view indicating a load which is applied to the pinion shaft of FIG. 10. As shown by FIG. 10 and FIG. 11, a pinion shaft 1 is configured with a pinion 4 downward from substantially a middle position in an axial direction thereof, and configured with a large diameter shaft portion 11 a diameter of which is larger than a gear tooth root circle diameter D1 of the pinion at an upper end of the pinion 4. Further, a lower end of the pinion 4 is configured with a small diameter shaft portion 12 a diameter of which is smaller than the gear tooth root circle diameter D1 of the pinion 4.
The large diameter shaft portion 11 is axially supported at a housing 3 by a ball bearing (first bearing) 21. A calk ring 22 is calked to be mounted to a ring-like groove 13 at an upper end of the large diameter shaft portion 11. An inner ring of the ball bearing 21 is squeezed between the calk ring 22 and an upper end face 41 of the pinion 4.
Further, an outer ring of the ball bearing 21 is inserted to a bearing hole 31 which is configured at the housing 3, and is fixed to the housing 3 unmovably in an axial direction by a snap ring 23 which is mounted to a ring-like groove 32 on a side of an opening of the bearing hole 31.
A gear tooth root 43 of the pinion 4 is piercingly machined with the gear tooth root circle diameter D1 staying as it is on a side of a lower end face 42 (small diameter shaft portion 12) of the pinion 4. Further, the gear tooth root 43 on a side of the upper end face 41 (large diameter shaft portion 11) of the pinion 4 is configured with a raised portion (first raised portion) 44 (a relief portion of a hob cutter in machining a tooth shape of the pinion 4) which has a radius R1 the same as a radius of curvature of the hob cutter on a side downward from the upper end face 41. Therefore, a distal end of the raised portion 44 is configured by a diameter the same as a gear tooth tip circle diameter D2 of the pinion 4.
A dimension of an outer diameter of the small diameter shaft portion 12 is configured to be smaller than the gear tooth root circle diameter D1 of the pinion 4 in order to avoid an interference between the hob cutter and an outer periphery of the small diameter shaft portion 12 when the pinion 4 is piercingly machined by the hob cutter in machining the tooth shape of the pinion 4. The small diameter shaft portion 12 is axially supported at a bearing hole 33 which is configured on a lower side of the housing 3 by means of a needle bearing (second bearing) 24. In this way, the pinion shaft 1 is supported at the housing 3 in a thrust direction and in a radial direction by the ball bearing 21 and the needle bearing 24.
An upper end of the pinion shaft 1 is connected to a steering wheel by way of a steering shaft, not illustrated. When the steering wheel is manipulated, a steering force thereof is transmitted to the pinion shaft 1. Rotation of the pinion shaft 1 is transmitted to a rack 5 by way of the pinion 4, and changes a direction of a steered wheel by way of a tie rod, not illustrated, which is connected to the rack 5. In order to smoothly transmit the rotation of the pinion 4 to the rack 5, teeth of the pinion 4 are configured by those of a helical pinion which has an angle of torsion relative to an axial center of the pinion shaft 1.
A rack guide 6 always presses a press block 61 to a back face of the rack 5 by an adjust cover 62. The adjust cover 62 presses the press block 61 to the back face of the rack 5 by urging the press block 61 by way of a coil spring 63. Thereby, there is eliminated a backlash of a portion at which the pinion 4 and the rack 5 are brought in mesh with each other to thereby smoothly move the rack 5.
As shown by FIG. 12, when a steering force of a steering wheel is transmitted to the rack 5, the pinion 4 is exerted with three kinds of loads of a thrust load P1, a radial load P2, and a tangential load P3.
The radial load P2 and the tangential load P3 are supported by the ball bearing 21 and the needle bearing 24, and the housing 3. However, the thrust load P1 is supported only by the ball bearing 21 and the snap ring 23. Therefore, when the large thrust load P1 is operated and the snap ring 23 is detached or broken, the pinion shaft 1 is moved in the axial direction, and therefore, the thrust load cannot be supported. Particularly, it is difficult to apply the configuration to a high output type of a column assist type electric power steering device or the like.
The rack and pinion steering device of Japanese Unexamined Patent Publication No. 2010-038254 prevents emittance of strange sound between a ball bearing and a snap ring, and does not prevent a movement in an axial direction of a pinion shaft by detachment or breakage of the snap ring. According to the rack and pinion steering device of Japanese Unexamined Patent Publication No. 2010-031915, a groove is configured at an outer ring of a ball bearing as a stopper against loosening of a screw cover which supports a thrust load of a ball bearing. However, the shape of the outer ring of the ball bearing becomes a special shape. Therefore, the manufacturing cost of the ball bearing is increased.